Hi,
I have been having this issue recently. I am using Ubuntu 19.10 (although it was happening before I upgraded from 19.04) I use a us-dvorak keyboard layout (but have tested it with us-qwerty) and happens whether I use copy-paste, a yubikey, or an onlykey (both of which I am using to output a static password). I have tried playing with adding delays to the outputs on these devices and that doesn't seem to help, but it does happen a lot more when using my hardward keys than when copy-pasting. I have tried English NZ,US, and UK as system languages and all have the same problem.